	URL
基本	https://qiita.com/cielavenir/items/9d068c49186060a47650
Pythonの.ssh/config読み出し	https://qiita.com/cielavenir/items/6aa9e6dc1166ae947c6f
大きいファイルの取得	https://qiita.com/cielavenir/items/f38223c156e4aaab58ad

Getting file object on SFTP.
The situation to get my authorized_keys is arbitrary.

Perl

sftp_file.pl

#!/usr/bin/perl
use strict;
use Net::SFTP::Foreign;
my $sftp = Net::SFTP::Foreign->new('localhost'); #,user=>$ENV{'USER'});
my $fh = $sftp->open('.ssh/authorized_keys',Net::SFTP::Foreign::Constants::SSH2_FXF_READ);
my $file_content;
for(<$fh>){$file_content.=$_;}
$fh->close;
print $file_content;
$sftp->disconnect;

Ruby

sftp_file.rb

#!/usr/bin/ruby
require 'net/sftp'
Net::SFTP.start('localhost',nil){|sftp| # ENV['USER']
	sftp.file.open('.ssh/authorized_keys','r'){|file|
		puts file.read
	}
}

Python

configで凝ったことをしている場合は https://qiita.com/cielavenir/items/6aa9e6dc1166ae947c6f が必要です

sftp_file.py

#!/usr/bin/python
#Py2/Py3 are supported
import os,sys
import paramiko
with paramiko.SSHClient() as ssh:
	ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
	ssh.connect('localhost') #,username=os.environ['USER'])
	with ssh.open_sftp() as sftp:
		with sftp.file('.ssh/authorized_keys','r') as f:
			sys.stdout.write(f.read().decode('utf-8'))